1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission comprising, metal ring assemblies each having a plurality of laminated endless metal rings, and a plurality of metal elements each having ring slots to which the metal ring assemblies are fitted, the belt being wound around a drive pulley and a driven pulley for transmitting a driving force between both of the pulleys.
2. Description of the Related Art
FIGS. 8A to 8C show a metal belt type continuous variable transmission, and show the shape of a compressed-side chord (chord between an outgoing side of a drive pulley 6 and an incoming side of a driven pulley 11) of a metal belt 15 wound around the drive pulley 6 and the driven pulley 11. FIG. 8A shows an ideal state in which the compressed-side chord is straight. In this state, the pushing force between metal elements 32 can be transmitted most efficiently, a load acting on inner circumferential surfaces of metal ring assemblies 31, 31 from saddle surfaces of ring slots of the metal elements 32 becomes small, and fatigue of the metal ring assemblies 31, 31 is reduced and the life thereof is increased. FIG. 8B shows a state in which the compressed-side chord is slightly warped outwardly (swelled radially outwardly). In this state, since the inner circumferential surfaces of the metal ring assemblies 31, 31 come into contact with the saddle surfaces of the ring slots under appropriate surface pressure, it is possible to stabilize the attitude of the metal element 32 in a rolling direction without lowering the durability of the metal ring assemblies 31, 31.
In contrast to the above states, FIG. 8C shows a state in which the compressed-side chord is slightly warped inwardly (swelled radially inwardly). In this state, since the inner circumferential surfaces of the metal ring assemblies 31, 31 float from the saddle surfaces (radially inward edges) of the ring slots of the metal elements 32 and come into contact with radially outward edges of the ring slots, the life of the metal ring assemblies 31, 31 is shortened, the metal elements 32 are rolled with respect to the metal ring assemblies 31, 31 and the attitude of the metal elements 32 becomes unstable, and there is a problem wherein vibration or noise is generated.
Further, it is known to increase thicknesses of portions of main surfaces of the metal elements to form contact portions, and to bring adjacent metal elements into abutment against each other through the contact portions to transmit the pushing force as disclosed in Japanese Utility Model Registration Publications Nos. 5-37067 and 5-5310 as well as Japanese Patent Publication No. 5-64254.
According to Japanese Utility Model Registration Publication No. 5-37067, three portions of a body of a metal element and two portions of an ear are made thicker than other portions to form a contact portion, and a neck connecting the body and the ear to each other is provided with elasticity, so that even if a drive pulley and a driven pulley are deviated or misaligned in the axial direction, the power can be transmitted in a direction perpendicular to the axis of the pulley, thereby enhancing the power transmitting efficiency.
According to Japanese Utility Model Registration Publication No. 5-5310, the compressive strain of a contact portion of a body located on a radially outer side from a locking edge of a metal element and the compressive strain of a contact portion of an ear are set substantially equal to each other so as to prevent fluctuation of attitude of the metal element when the latter transmits the pushing force, thereby enhancing the power transmitting efficiency.
Further, according to Japanese Patent Publication No. 5-64254, two portions of a body of a metal element, one portion of a neck and two portions of an ear are made thicker than other portions to form a bilaterally symmetrical contact portion. The displacement characteristics between the metal elements due to a pushing force and the compliance value of a compressed-side chord of a metal belt are made approximately consistent with each other, thereby providing the metal element itself with stable straight properties and displacement characteristics appropriate to misalignment levels.
However, in Japanese Utility Model Registration Publication No. 5-37067 and Japanese Patent Publication No. 5-64254, the shape of the metal element is devised for absorbing the misalignment, and the radial warp of the metal belt of the compressed-side chord is not taken into account at all. Further, Japanese Utility Model Registration Publication No. 5-5310 is aimed at keeping the compressed-side chord of the metal belt straight and therefore, there is a problem that the excellent state (see FIG. 8B) of the metal belt in which the compressed-side chord is slightly warp outwardly can not be allowed and flexibility in design of the contact portion of the metal element is limited.
The present invention has been accomplished in view of the above-described circumstances, and it is an object of the present invention to obtain an appropriate warp shape of a compressed-side chord of a metal belt by appropriately locating the contact portion at which metal elements come into contact with each other.
To achieve the above object, according to a first feature of the present invention, there is provided a belt for a continuously variable transmission comprising, metal ring assemblies each including a plurality of laminated endless metal rings, and a plurality of metal elements each having ring slots to which the metal ring assemblies are fitted. The belt is wound around a drive pulley and a driven pulley for transmitting a driving force between both the pulleys. A main surface of each of the metal elements is formed at portions thereof with contact faces for transmitting a compression load in the fore-and-aft direction, with the radial position of the centroid of the contact faces being set between the center in a thickness direction of the metal ring assembly fitted into the ring slot and the radial outer edge of the ring slot.
With the above structure, since the radial position of the centroid of the contact faces formed on portions of the main surface of the metal element, is set between the center in the thickness direction of the metal ring assembly fitted into the ring slot and the radial outer edge of the ring slot, a compressed-side chord of the metal belt can assume a straight shape or a slightly outwardly warped shape, and it is possible to elongate the life of the metal ring assemblies, to reduce noise and vibration, and to enhance the power transmitting efficiency.